Study of Long Term Cosmic Ray Daily Variation

The average diurnal variation of cosmic rays at neutron monitor energies vary with a period of eleven and twenty two years. Moreover, the annual average comprises of days with significant departure from the observed average amplitude and time of maximum. Consecutive days with very low amplitudes as well as of very high amplitudes have been identified earlier also, for which many investigators have reported the characteristic properties of such waves. However, they are not consistent and no characteristic and no reliable interplanetary parameter could be associate with these waves. In order to understand the occurrence of these waves during solar cycle 22, the data from a number of neutron monitors have been analyzed and average characteristics for each event has been derived in a manner as was done in the past by us for the earlier solar cycle. We find that the first harmonic of high amplitude days usually have zero spectral exponent. Moreover the second harmonic of high amplitude days show “0” spectral exponent in contrast to “I” expected. A few specific events of longer duration support these statistical conclusions. However, from the available limited interplanetary data, no specific parameter is identifiable either for the low or high amplitude wave trains.